The Global Change Observation Mission (GCOM) is a concept comprised of two polar-orbiting satellite series, spread over three generations to achieve long-term and consistent observation of the Earth. The two satellite series are GCOM-W (Water) and GCOM-C (Climate). GCOM aims to monitor climate variability and water-energy cycle, focusing on the observations of radiation budget, carbon cycle, and water-energy cycle. Scientific and practical importance of these targets are evident. Changes of cloud and aerosol and the radiative forcing are the major uncertainties in the climate modeling. Providing the information on carbon dioxide sources and sinks is necessary for complete understanding of the global warming. Water, which has direct influences on human activities through severe weather, drought, floods, and changes of water resources, is an important observation target. Long-term and continuous observation is not only necessary for monitoring climate variability, but also essential to make the satellite observing system a part of our social infrastructure through the development of various operational applications. Cooperation with numerical prediction models is highly expected to contribute to various levels of decision-making. For short-term weather forecasting, satellite observations are becoming an indispensable data source to generate better initial values through data assimilation techniques. For long-term climate prediction, although it seems to be still limited, it is expected that satellite data can potentially be used for global-scale validation of model outputs. GCOM-W1 and GCOM-C1 are the first generation of satellites. Each one is a medium-size, polar-orbiting satellite with a single observing instrument. This is to reduce the risks associated with a large platform that contains multiple important instruments. Space-proven components and parts are used to the maximum extent to enhance the reliability of the satellite system. Also, a common design for the satellite bus are used to minimize the total cost of the system. GCOM-W1 carries the Advanced Microwave Scanning Radiometer-2 (AMSR2) and GCOM-C1 is equipped with the Second-generation Global Imager (SGLI). This combination of multi-purpose instruments enables us to cover a wide range of geophysical parameters by GCOM. AMSR2 will perform observations related to the global water and energy cycle, while SGLI will conduct surface and atmospheric measurements related to the carbon cycle and radiation budget. AMSR2 will extend the observation of currently ongoing AMSR-E on EOS Aqua platform. Current target launch dates are Japanese fiscal year (JFY) 2011 for GCOM-W1 and JFY 2014 for GCOM-C1. Since the long-term and comprehensive observation of the Earth can not be effectively addressed by each country or by a single mission, international and inter-mission cooperation is essential. The cooperation between the National Oceanic and Atmospheric Administration (NOAA) and JAXA for the Joint Polar Satellite System (JPSS) and GCOM is a case example of this kind of cooperation.

GCOM-W1 will participate in the A-Train satellite constellation to enhance the scientific capability through the synchronous observations with other instruments available in A-Train, and also to assure the cross-calibration with AMSR-E, which is also in A-Train. AMSR2 is a multi-frequency, total-power microwave radiometer system with dual polarization channels for all frequency bands. The basic concept is almost identical to that of AMSR-E. The frequency bands include 6.925, 7.3, 10.65, 18.7, 23.8, 36.5, and 89.0 GHz. The 7.3 GHz channels are added to help mitigate the radio-frequency interference in 6.925 GHz channels. Diameter of the deployable antenna is increased from 1.6 m (AMSR-E) to 2.0 m. Intensive efforts were made for improving the high temperature noise source (warm calibration load) from the aspect of the thermal design. Development of GCOM-W1 system is progressing favorably despite the slight delay caused by the earthquake on March 11, 2011. In summer of 2011, several tests will be performed and the pre-shipment review is planned in late October 2011. Development of the ground segment will also be completed in summer 2011. The standard products from AMSR2 include eight geophysical parameters. The standard algorithms for daily processing had been developed and selected with the collaboration of the principal investigators. These algorithms will be validated and updated during the initial calibration and validation phase. As an instrument calibration activity, a deep space calibration maneuver is planned during the satellite commissioning phase.

GCOM-C1 will be placed in the orbit at an altitude of about 800 km and at a local time of descending node of 10:30, to maintain a wide observing swath width and reduced cloud cover over land. The SGLI instrument has several unique features: 250 m spatial resolution for most of the visible channels, 250/500m resolution for thermal channels, and polarization/multidirectional observation capabilities. The 250/500m spatial resolution will provide enhanced observation capability over land and coastal areas where the influences of human activity are most evident. The polarization and multidirectional observations will enable us to retrieve aerosol information over land. SGLI consists of two major units: the Infrared Scanner (IRS) and the Visible and Near-infrared Radiometer (VNR). VNR can be further divided into two sub-units: VNR-Non Polarized (VNR-NP) and VNR-Polarized (VNR-P). VNR-P is a polarimeter with three polarization angles (0, 60, and 120 degrees) and a tilting function (±45 degrees in along track direction). From the information gathered by the 19 channels of SGLI, considerable number of products will be produced. Testing of the GCOM-C1 satellite mechanical test model is underway, followed by the thermal balance testing of the thermal test model. The SGLI EM test is performed to confirm the electrical/optical performance. Critical design of the satellite is progressing toward the critical design review planned next year.